 let arr = ['后盾人']
 console.log(arr)
 console.log(arr.concat)
 var c = Object.getOwnPropertyDescriptor(arr.__proto__, 'concat')
 console.log(c)
 console.log('-----------------------\n')
 
 var c = Object.getOwnPropertyDescriptor(arr, 'length')
 console.log(c, arr.length)
 
 var c = Object.getOwnPropertyDescriptor(arr.__proto__, 'length')
 console.log(c, arr.length)
 